Previous research has shown that the only effect an environment has on the development of a language is vocabulary. However, a new study published in the open-access journal PLOS ONE suggests that altitude can influence the used of ejective consonants in a language.

Not used in the English language, ejective consonants are made by compressing air in the pharynx and then releasing it, resulting in a popping or guttural sound.

“This is really strong evidence that geography does influence phonology — the sound system of languages,” said the study´s author Caleb Everett, an associate professor of anthropology at the University of Miami.

Everett found that 87 percent of the ejective-containing languages included in the study are located within 300 miles of a high-elevation region, regardless of the continent. The anthropologist also found a direct relationship between increasing elevation and the likelihood of a language containing ejectives.

“I was really surprised when I looked at the data and saw that it correlated so well,” Everett says. “It really does not rely very much on my interpretation, the evidence of a relationship between altitude and language is there.”

In his study, Everett analyzed the locations of about 600 representative languages, about 8.6 percent of the world´s languages. Fifteen percent of these languages contained ejectives. Using the World Atlas of Linguistic Structures, Everett superimposed the coordinates of these languages onto the world’s landscape to analyze geographic patterns. He then focused his study on the six major inhabited high-elevation regions in the world: “¯the North American Cordillera, the Andean region, the southern African plateau, the plateau of the east African rift and the Ethiopian highlands, the Caucasus region and Javakheti plateau; and the Tibetan plateau.

An analysis of this phonology map revealed a strong correlation between high altitude and the use of ejectives on, or near, five of the six major high altitude regions on earth where people live. The only exception was the large Tibetan plateau and the adjacent areas.

“Since air pressure decreases with altitude and it takes less effort to compress less dense air, I speculate that it’s easier to produce these sounds at high altitude,” Everett said.

Because the body uses non-pulmonic techniques to create ejective consonants, their use decreases the amount of air exhaled from the lungs and therefore the potential for dehydration in high altitudes, the study said. Non-pulmonic techniques are those that are not produced using air pressure from the lungs.

Previous research has shown that Tibetan people breathe more rapidly than other high altitude populations. This theoretical adaptation to the climate results in a lessening of the effects of hypoxia in high altitude. Everett suggested that this unique adaptation may account for their exclusion from the ejective consonant group.

Although it only examined a fraction of all the languages spoken on Earth, the study represents the first link between geography and the sounds used in a language. It could set a precedent for other language researchers looking to make similar connections. For example, there could be a similar correlation between certain sounds and lower elevations.

Everett said he is currently looking into other connections between geography and linguistics.